Series URL repair: owner-typed, gated by the poller's own fetch gate (#151)

backend/internal/latest/read.go

@@ -41,7 +41,7 @@ var (
 // its own network position to whatever URL a token-holder writes, including
 // link-local/internal addresses or non-https schemes.
 func readSeriesPage(ctx context.Context, site, seriesURL string, browser, tls Fetcher) (seriesRead, error) {
-	if !fetchableSeriesURL(site, seriesURL) {
+	if !FetchableSeriesURL(site, seriesURL) {
 		return seriesRead{}, fmt.Errorf("%w: site=%q url=%q", errNotFetchable, site, seriesURL)
 	}
 	f := fetcherFor(site, browser, tls)